Patent GB-440089-A (GB)
Title: Improvements in and relating to colour photography
IPC: G03C7/26
Filed: 1934-06-15
Abstract: 440,089. Colour photography. KODAK, Ltd., Kingsway, London.-(Eastman Kodak Co. ; 343, State Street, Rochester, New York, U.S.A.) June 15, 1934, No. 16013/35. Divided out of 440,032. [Class 98 (ii)] A photographic element having distributed between the front and rear sides of a single support at least three gelatine-silver halide emulsion layers containing superimposed latent image records of different colour sensations substantially covering the whole of the visible spectrum is processed to a natural colour photograph by producing reversed silver salt images in all the layers, simultaneously rendering developable at least all of the images on that side of the support which carries more than one layer, preferably by exposure to light, and thereafter processing each image to the minus colour of the primary colour of which the image is a record. A film may comprise a cellulose acetate or nitrate support carrying on the rear side layers of red-sensitized emulsion, colourless or red or green gelatine, and greensensitized emulsion, and on the front side layers of yellow-coloured gelatine and blue-sensitive emulsion, and, if desired, a transparent waterproof stripping layer of benzyl cellulose. The green-sensitized emulsion may have an antihalation backing and is sensitized with erythrosin, and the red-sensitized emulsion is sensitized with naphthocyanol. Suitable yellow dyes are tartrazine, quinoline yellow or brilliant yellow. A colourless gelatine layer may be interposed between the yellow layer and the blue-sensitive layer. Gelatine-silver bromide emulsions are employed. The film is tanned, developed in the dark with a metol-hydroquinone developer containing potassium thiocyanate and formaldehyde, washed, treated in a reversing bath containing potassium permanganate and sulphuric acid, washed, cleared in a sodium bisulphite bath, washed, exposed to white light, colour developed to minus red in a developer containing p-aminodiethylanilinehydrochloride, potassium thiocyanate, and m hydroxydiphenyl, fixed, washed, and thoroughly dried. Further processing is carried out in the light. The top layer on the rear side of the support and the single layer on the other are bleached in a bath containing quinone, hydrobromic acid, glycerine and iso-propyl alcohol or containing chromic acid and methanol. The film is immersed in a stop bath containing sodium bicarbonate, isopropyl alcohol and glycerine or containing sodium bisulphite. The film is washed and the two bleached layers colour developed to minus green in a developer containing 2-amino- 5-diethylaminotoluene hydrochloride, potassium thiocyanate, p-nitrophenylacetonitrile and isopropyl alcohol. The rear side of the film is covered with a benzyl cellulose varnish, and the single layer on the front side bleached and colour developed to minus blue in a developer containing p-aminodimethylaniline sulphate, 4-nitroacetoacetanilide, and iso-propyl alcohol. The varnish coating is stripped off, the metallic silver removed by Farmer's reducer and the film washed and dried. In a modification the second colour development is to minus blue and the varnish layer is applied to the front of the film. In further modifications all the reversed images are colour developed to minus blue, the film is fixed and the single layer is given a strippable varnish coating. The two layers on the rear side are developed to minus red, and the top layer is bleached and colour developed to minus green. Alternatively, the upper layer only is developed to silver using a developer containing a large amount of sodium sulphate followed by a stop bath containing sodium sulphite and acetic acid at 0 to 5‹ C., the lower layer is colour developed to minus red, and the upper silver image is bleached in a potassium ferricyanide bath and colour developed to minus green. In a further modification the upper reversed image is colour developed to minus green by controlled penetration, thoroughly dried, and the bottom layer colour developed to minus red. In a further modification the whole of the reversed images are developed to silver, fixed, washed, bleached to silver ferrocyanide and dried. The varnished layer may be dispensed with by using the flotation process. In a further modification the film is initially provided with a strippable varnish coating on the front side. Reversed silver halide images are produced in the two layers on the rear side, exposed to white light, colour developed to minus red, and fixed. The top image is bleached, exposed to white light, colour developed to minus green, and fixed. The varnish-layer on the front side is stripped off, the latent image developed, reversed, exposed to white light, colour developed to minus blue and fixed, and residual silver removed from all the layers. Reversed images may be rendered redevelopable by treatment with chemical reagents. When two images have been colour developed, the third silver image may be coloured by mordanting and dye-toning. The film may carry a sound track. The process may be applied to a film having three layers on one side and one on the other. Specifications 176,357, 245,198, [both in Class 98 (ii)], 327,714, 333,902, [both in Class 2 (ii)], 341,183, 356,308, 376,838, 427,472, 427,516, 427,518, and 427,520 are referred to.